Whenever the fuel tank or the fuel line of an engine is exposed to cold weather, the fuel or certain impurities or additives contained in the fuel may gel or "wax". The viscosity of the fuel, additives, or impurities increases to such a degree that the fuel no longer flows well through the fuel systems. For example, the diesel fuel in the fuel tanks or fuel lines of diesel trucks may wax if the truck is parked or driven in extremely cold weather. Since waxing can interfere with the proper flow of fuel to the engine, it frequently results in poor engine performance. Severe waxing may even block the flow of fuel entirely, stalling the engine.
Similar cold weather problems exist with the use of hydraulic oil. Typically hydraulic oils of various grades experience viscosity changes dependent on temperature. In cold weather or winter months, hydraulic oil which is cold provides slower response times to the equipment it is powering. It is often necessary to warm the hydraulic oil reservoir prior to powered operation of equipment to avoid improper operation.
Problems also exists when diesel fuel or hydraulic oil is warmer than an optimum operating range. In the case of diesel fuel, optimal operating temperatures may range generally between about 60.degree. F. and about 110.degree. F. subject to the quality of the diesel fuel, additives therein, and other considerations. Frequently, diesel fuel in trucks and vehicles operating in warmer climates or for long durations produce heating effects within the engines that cause the fuel temperature to exceed the optimum power ranges. This overheating may result in numerous problems, including damage to electronic components in engine systems. Therefore, it is desirable to reduce the amount of heat in the fuel in such situations. Similarly, when hydraulic oil is warmed beyond an optimum range, power control problems and residual heating effects may occur. It is, therefore, desirable to reduce the amount of heat in hydraulic oil reservoirs when the temperature of such reservoir exceeds a predetermined range, but at the same time be able to provide good heat rise to such fluids as warranted.
In addition, fuel frequently becomes contaminated with water. Sometimes water contaminants are already present in fuel when the fuel is added to the fuel tank. Improper handling or poor refining may introduce water contaminants to fuel. Moreover, water condensation inside a fuel tank sometimes takes place following outside air intrusion into the fuel tank. At low temperatures, water contamination can take the form of ice crystals suspended in the fuel. Fuel contaminated with water or ice crystals also causes poor engine performance or stalling.
Cold weather operation of vehicles and other equipment is also adversely affected by the loss of power in a battery used for providing startup power to the system. This is a particularly debilitating problem in severe cold weather or very low temperature wind chill environments during extended vehicle shut off periods, such as overnight shut downs.
Numerous methods and apparatus have been used in the past in an attempt to solve these or related problems. Waxing and system thermal loss may be eliminated by heating the fuel and related components. Also, heating the fuel melts ice crystals and tends to cause water contaminants to precipitate from the fuel. Although heating fuel may eliminate waxing or icing, the water, in liquid form, may collect within the fuel system, for example, inside the fuel tank or inside a fuel filter disposed downstream from the fuel tank.
There have been many proposed devices for heating fuel to eliminate waxing and icing, to precipitate the water, and to purge water from the fuel system. Many such devices employ tubes which circulate a heatable fluid, for example, a fluid bearing waste heat, such as engine coolant, motor oil, or exhaust gas, through a reservoir of fuel. Typically, the fuel is then heated via a heat exchange process, as shown for example, in U.S. Pat. No. 4,553,697 issued to Nothen, U.S. Pat. No. 2,641,451 issued to Kaiser, and U.S. Pat. No. 4,964,376 issued to Veach et al. However, it frequently requires a considerable period of time for the coolant or exhaust gas to become hot and for the hot coolant or exhaust gas to sufficiently heat the fuel and other system components. Consequently, the engine may nonetheless perform poorly for a long period of time, and might even subsequently shut down unexpectedly.
Further, while much of the fuel is eventually heated by such a device, localized cold spots may still develop. For example, in the extremely cold weather, the fuel may continue to wax along the bottom and sides of large metal fuel tanks. Since the inlet of the fuel line is typically located near the bottom of the fuel tank, such localized waxing along the bottom of the tank may interfere with the proper flow of fuel through the fuel line. In similar manner, oil drain pans experience related cooling due to their normal location beneath engines.